Electron emitting element



Patented Jan. 9, 1934 1,943,021 ELECTRON EMITTING ELEMENT Hector Rabezzana, Flint, and Ora S. Dufiendack, Ann Arbor, Mich, assignors to A Spark Plug Company, Flint, Mich, a companyof Michigan No Drawing. ApplicationMarcli 2, 1931, Serial No. 519,675, and in Great Britain October 11,

This invention relates to electron emitting elements and compositions therefor. The application is a continuation in part of our prior application Serial Number 302,904, filed August 30,

In that application there is set forth the well known problem of short-circuiting of plugs by carbon deposit on the insulators, and the fact that a plug having a high sparking voltage will become fouled much more quickly than one having a low sparking voltage. By sparking voltage is, of course, meant the voltage required to cause a spark to jump the gap between the spark plug electrodes in the combustion chamber.

We have also set forth in that application our discovery that, contrary to accepted beliefs, the sparking voltage varies with the composition of the electrodes, and have disclosed a number of substances which, when incorporated in the spark plug electrode, have the effect of materially reducing the sparking voltage. While the class of substances having that property is broadly claimed in that application, the present application is directed to the use of one of the substances for spark plug electrodes and similar electron emitting elements, as well as to the preferred form of alloy in which the element is incorpo rated.

To be commercially usable for incorporation in spark plug electrodes to reduce the sparking voltage, the substance must, as set forth in our said prior application, possess a low work function. By work function is meant the amount of work necessary to remove an electron from the element. In addition the substance must be capable of being easily alloyed with other elements such as nickel which it is desirable to include in the alloy from the point of view of electrical conductivity and resistance to heat and corrosion. i

From this standpoint among the most desirable of the substances mentioned in our prior application is the element calcium.

This element alloys well with nickel, forming a true solid solution in which the calcium is uniformly distributed. Itmaterially reduces the sparking voltage, and the resultant alloyis resistant to heat and corrosion. The alloy is also fairly permanent so that the advantage of low sparking voltage will continue over a long period of time. By permanent alloy it is meant that the added ingredient does not readily evaporate from the base metal during the operation of the plug. While a nickel-calcium alloyresists heat and corrosion to a fair degree it is necessary to .but the amount of these metals is so slight as 1 Claim. (01. 15-1).

and the can is immersed in the molten nickel or nickel-manganese alloy. The foil or the iron and tin, of which the can is composed, are melted and become mixed with the other ingredients 7 to have practically no effect on the alloy. The advantage of this method of preparing the alloy is that the calcium is kept out of contact with the air and becomes alloyed with the nickel and manganese before it has opportunity to oxidize. By this method of preparation we have found that the calcium is uniformly distributed throughout the alloy in practically the same proportions in which it is added to the melt.

A preferred composition of alloy for spark plug electrodes is given below:

Percent Calcium .04 to .10 Manganese 2 Magnesium a trace Nickel balance There is nothing critical about the proportions of the ingredients except that the calcium should be in excess of 114% of the total to insure that it' will have an appreciable efiect in reducing the sparking voltage. In actual practice the quantity of calcium used will be considerably in excess of this amount. In general the reduction in sparking voltage will within certain limits increase in proportion .to the amount of the low work function element that is added.

The amount of magnesium present in the al- 10y is so small, so difficult tomeasure by ordinary methods of chemical analysis, and so nonuniformly distributed that it has been designated as a trace. It is the residue of about .1% magnesium added to deoxidize the alloy and increase its ductility so as to permit easy drawing.

The upper limit of calcium is merely the maximum that we have so far succeeded in obtaining in. our melts. It is expected that by improvements in furnace technique it will be possible to include larger amounts. One improyement which should help is the time control method of satisfactory,

preparation of alloys as described and claimed in the copending application of D. W. Randolph, Serial No. 520,704, filed March 6, 1931.

Electrode material including low work function elements is not confined in its utility to spark plugs. Compositions characterized by ease in giving off electrons are also very desirable for use in the manufacture of electrodes for vacuum tubes such as are used in radio work and in current rectifiers; also in luminous vapor lamps such as the well known Cooper-Hewitt mercury vapor lamp; and in luminous gas lamps, such as the well known neon tube, and the like. Many other uses will occur to those skilled in the art.

For other uses, as in vacuum tubes, larger percentages of calcium are desirable. For this use also manganese may be omitted. Here the base metal serves chiefly to provide mechanical support for the electron emitting material, and corrosion is not a factor.

Instead of using nickel as the base metal we may use cobalt, an element of well recognized similar characteristics. Cobalt will not be as however, for spark plug work, where corrosion is a factor, for it has relatively .poor corrosion resisting properties.

Elsewhere its use may be desirable. In the claim we have grouped nickel and cobalt together under the term nickel-cobalt metal.

We have also made and tested alloys of calcium with copper, with silicon and with chromiurm The copper-calcium alloy is 'not as resistant to corrosion as is desirable for spark plug work. The same is true of the silicon-calcium alloy. We have also found that silicon has a bad effect on emission. The calcium-chromium alloy has roven to be unworkable by ordinary drawing methods because of its extreme hardness and lack of ductility.

We claim:

An electron emitter homogeneous throughout made of an alloy characterized by ready electronic emissivity, ductility and resistance to heat and corrosion comprising a solid solution of calcium and nickel, calcium constituting from .04% to .10% of the total and the balance consisting essentially of nickel, and approximately 2% manganese;

HECTOR RABEZZANA. ORA S. DUFFENDACK. 

